


Good Vibrations

by rehliamonster



Series: Prostitute Sans Series [2]
Category: Undertale (Video Game)
Genre: Begging, Crying, Ecto-Genitalia (Undertale), Fingering, Kink Negotiation, Light Dom/sub, M/M, Massage, Multiple Orgasms, Multiple Penetration, Oneshot, Orgasm Delay/Denial, Overstimulation, Plot What Plot/Porn Without Plot, Praise Kink, Prostitution, Size Difference, Size Kink, Teasing, Vibrators, Voluntary Prostitution, Wet & Messy, bone stimulation, sacrum stimulation, sans is a prostitute
Language: English
Status: Completed
Published: 2018-03-05
Updated: 2018-03-05
Packaged: 2019-03-27 14:38:08
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,486
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13882965
Author URL: https://archiveofourown.org/users/rehliamonster/pseuds/rehliamonster
Summary: Sans gets paid to help Mettaton test some new "equipment."He loves his new job.





	Good Vibrations

The room was just like Sans remembered it: grand to the point of gaudiness, dominated by a hilariously big bed, and having way too many Mettaton-shaped decorations. 

As if he wasn’t going to see enough of the guy already. 

He hopped up onto the bed, leaving his slippers behind in a haphazard manner and getting comfortable on the bedspread in a cross-legged position, facing the door. Mettaton was currently busy locking it before turning towards him with an appraising expression. 

“want me to get undressed right away or do you wanna do that?” Sans asked calmly. 

“You can get undressed,” Mettaton told him immediately, beginning to shift into his more human-like form. He often did that, despite how much energy it took out of him. But according to Mettaton, his human form was more convenient for this. 

Sans didn’t mind either way. 

Sex with Mettaton was mostly different variations of colourful vibrating appendages being shoved against his bones or various conjured genitalia, regardless of whether those appendages were attached to a box or the simulacrum of a human. The sensations were the same anyway, and Sans was never one to care all that much about outer appearances.

Stripping down quickly, he carelessly tossed his clothes aside on the floor. That was one positive thing about being pretty sloppy in general; it meant that even if he ended up looking rumpled or slightly messy as a result of his escapades, it wouldn’t be out of the ordinary and thus was less likely to be noticed. 

Mettaton was already done shifting when Sans was finished, looking at him with a thoughtful expression on that carefully modelled face. 

“Lay back,” Mettaton finally said. 

Sans obeyed and shifted back on the bed, coming to a rest on his back with his tibia and fibula dangling over the edge of the bed. Pretty standard. 

Mettaton kneeled down in front of him, appraising his bones without touching them yet, hovering a hand just about Sans’ pelvis. Sans knew why. It wasn’t common knowledge throughout the Underground, but Mettaton had a bit of a size kink. It was part of the reason why his constructed body was so tall in his human-like form. He got a kick out of being bigger than most other monsters.

“The safeword is the same as always?” Mettaton asked after a moment, looking up to Sans’ eyes. 

“yeah, nothin’ new here,” Sans confirmed. “you?”

“Mine hasn’t changed either,” Mettaton stated calmly. 

Mettaton’s safeword was more a formality than anything else; Sans wouldn’t actually be doing anything other than laying here and letting Mettaton do anything he wanted until he was satisfied. Almost anything he wanted. 

There were some rules of course: Mettaton had to do the physical work, and there would be no pain or dangerous practises. Sans didn’t like being active much and with his low health, he preferred to stay clear of anything involving pain and risk. Other than that though, he was pretty much game for any weird kink his clients could think of. 

The final rule was that Papyrus would never find out about Sans’ activities. He always communicated these rules clearly to his clients the first time, and trusted them to be followed. The community of clients and prostitutes in the Underground was tightly knit but also an open secret - most monsters were at least somewhat aware that these activities existed, even if they didn’t know who exactly was involved. And so ratting someone out was generally followed by being shunned by the whole population. If you couldn’t keep your mouth shut, you didn’t deserve taking part, simple as that.

But Mettaton knew all of that. After all, the entertainment robot was the reason why Sans had become a prostitute in the first place. 

Running up inordinately large tabs was a bad habit that Sans really tried to get rid of, but he had trouble managing. His good old friend Grillby had supported him and always cut him off before his debts had gotten to a point of not being manageable anymore. Mettaton however had a lot of other stuff to do, so by the time he got around to ask Sans to pay up, Sans simply couldn’t. It was way too much. 

Initially Sans had been pretty worried about the consequences, but it turned out Mettaton was actually a fairly reasonable guy under all the dramatic flair. He had offered Sans a gig as a stand-up comedian at the hotel to work off his debt, and when it became clear that this alone wouldn’t take care of the massive debt any time soon, he had offered other options. Security, cleaning, room service, reception, sex. 

The latter had been mentioned just as casually as all the rest. 

When Sans had asked about it incredulously, Mettaton had merely laughed and explained that there was a whole group of monsters in the Underground prostituting themselves for a variety of reasons. Pleasure, paying back debts, saving up for large purchases, loneliness; the list of reasons for doing it was just as long as the list of reasons for employing a prostitute. 

They all set their own rules in terms of what they would and wouldn’t do, but generally had at least two rules in common. For once, all prostitutes would make sure to keep their prices within a certain range, charging extra only for services that nobody but one specific prostitute could perform. And secondly, it was expected to keep a lid on the whole affair. The prostitutes wouldn’t rat each other or their clients out, nor would the clients say a peep about whom they were hiring. It was a system that worked on referrals and secret code-words and the like; either you knew who was offering what, or you didn’t. 

After explaining that, Mettaton told Sans very clearly that if Sans didn’t want to do sex work, he didn’t have to. There would be no pressure and no extortion whatsoever. They could find other ways to take care of that massive debt. 

Sans felt intrigued, however. If he could set his own rules, then that pretty much meant that he could set physical activity as one of his boundaries. 

Which meant that he could literally be paid to lay back and do _absolutely nothing_. 

Shit, he’d get paid for being fucked, for maybe coming a couple of times a day. 

That sounded pretty much like his dream job, so he told the robot that he’d try it out. Mettaton got him into contact with one of the other prostitutes, who got him into contact with a client. Sans found he liked it just as much as he thought he would, and the rest was history. He started working and with that new job, it turned out to be surprisingly easy to pay Mettaton back, and a couple of other debts he had accumulated too. His tab at Grillby’s, gambling debts with Doggo, outstanding bills to the community for energy, the mortgage on the house, outstanding payments to Muffet - for the first time in a long while, it was all taken care of. 

Sans could have stopped then, but he liked his new job so much that he kept going, using the money he earned to add to Papyrus’ car savings and to buy ketchup and other luxuries for himself. He enjoyed being able to just buy shit whenever he felt like it, without having to worry about being indebted to someone. The fact that he got easy orgasms out of it without ever having to go through the effort of wooing someone or otherwise making much of an effort was just the cherry on top.

It was a good life. 

Between his legs, Mettaton was carefully inserting his hand through Sans’ pelvic inlet, making sure not to tough the bone just yet. Sans held as still as he could, feeling intrigued as he looked down. He had a desire to squirm even though he wasn’t being touched - it felt _weird_ to have something go through that opening, as if he should be able to feel it but couldn’t, hovering on the precipice of stimulation without receiving it. 

A soft click resounded from somewhere inside Mettaton’s body, and the arm and hand began to vibrate faintly. 

Sans could feel it, even though he still wasn’t being touched. 

“shit,” he blurted out, his breath practically exploding out of him. He hadn’t even noticed that he had begun holding his breath. 

Mettaton chuckled, a high sound without the affected tone he normally used while talking. He just sounded amused, and as if he was enjoying himself. 

“please,” Sans whined, knowing that begging would get him what he wanted. “please, please make me feel good, you’re so good…”

Praise and submission, that was always a winning combination with Mettaton. The robot was self-admittedly narcissistic and enjoyed being told how good he was, and the idea of people debasing themselves for his sake. 

“Of course, darling.”

Sure enough, Mettaton gave him a smug smile before he lowered his vibrating hand and trailed the buzzing fingers over the sensitive holes in his sacrum. The sudden switch from gentlest teasing to direct stimulation on one of his most sensitive body parts had Sans scream out and arch his spine, squirming in a desperate bid to… well, what? Getting away, or getting closer? He wasn’t entirely sure himself, mind fuzzing over in the onslaught of sensation. 

Mettaton’s fingers were too large compared to Sans’ sacrum holes to fit in there, but he had underestimated the other’s creativity and drive to improve and modify his own body. Another click was audible, and then panels slid away from the tips of Mettaton’s fingers, allowing thinner appendages to emerge from the openings underneath. Slender bottle brushes with the softest of hairs - Sans could feel just how soft those bristles were in perfect clarity against his sacrum, before the brushes slid into the two lowest sacral holes. 

He screamed as he came immediately and almost painfully.

Embarrassingly high-pitched and drawn out, staring in disbelief at the brushes vibrating inside of his bone, the buzzing motion of each individual hair against the inside of the sacral holes a delicate torture of the highest order. His pelvis twitched and his legs were trembling, while his mouth hung open, dripping saliva onto his own ribcage. 

Just when he wanted to kick out and scramble back because the stimulation was getting too much, Mettaton withdrew out of his own volition. He didn’t stop the vibration on his arm and hand, but he didn’t touch Sans, giving him a moment of respite to come down from his high. 

“fuck, fuck, what the fuck,” he blabbered, still staring at his sacral holes. They were tinted a light blue, the sudden and intense stimulation having gathered the magic there. He could feel it throb there, confused whether he was in pain or not. 

He was not. 

Mettaton was sticking to Sans’ rules. It was a close thing, but getting his sacral holes brushed out fell _just_ on this side of pleasurable. 

“Too much?” Mettaton’s voice was sensual and clearly aroused, but the concern was genuine. He could be a dick, but not this much of a dick. When it came to their sexual exploits, he was aware of the relative position of power he was in due to how he had gotten Sans into this line of work, and how despite the fact that the debt was paid off, the power imbalance the debt had created in the first place was still very much mentally present. 

“it’s fine,” Sans managed to huff. “but warn me next time.” 

“I shall,” Mettaton declared. “Scrubbing those nooks of your bones seems interesting. Could I do the rest?”

Sans allowed himself to take a moment to really think about it. Now that he had gotten over the first shock and the aftermath of the sudden orgasm, he felt kind of curious about this idea. 

“make the vibrations milder, please,” he asked. 

“As you wish, sweetheart.” 

The brushes approached his sacrum again, now moving in a slower, more gentle pattern. When they touched the bone and the soft hairs began to massage the dips and ridges surrounding his sacral holes, Sans couldn’t help the deep moan slipping through his teeth. It was ticklish and hellishly soft, but the mild pressure that Mettaton applied ensured that it felt pleasant at the same time. It did remind him of his usual bathroom activities when he used a variety of scrubbing brushes and toothbrushes to make sure he got clean. He often couldn’t be bothered to do the full routine, but he did it every once in a while. He wasn’t a complete slob after all, only a bit of one. 

Fuck, he’d never be able to clean himself again without thinking of this. 

“What a beautiful face,” Mettaton commented, practically purred as he leaned over Sans, trailing the brushes closer to the sacral holes again. 

Sans very much doubted that, considering that he still had his mouth hanging open, uncaring of the saliva that trailed down his body. He must look like an idiot. 

He couldn’t bring himself to care. 

Not when the brushes were slowly, ever so slowly being dipped into the next holes of his sacrum again, making his bones twitch and shudder. He moaned again, feeling his magic prickle on the bones of his pelvis. Something sparked and sputtered out immediately; there wasn’t enough space in his pelvic inlet at the moment for what his body was trying to manifest. Mettaton’s arm was taking up all the available space. 

Sans felt his magic spasm before it rushed forwards, gathering on his pubic bone instead in the form of a hardened cock. There was precum already leaking from the tip in generous amounts; the brushes weren’t as shocking in his sacral holes now as the first time, but he still knew he was close to coming again. His lower body rocked forwards, desperately trying to find more stimulation, but there was nothing to grind against. 

“fuck, please… fuck, fuck me, please,” he huffed, having trouble stringing the words together. 

“I _have_ been wanting to try all these new modifications out, I suppose,” Mettaton allowed, making it sound as if he was doing Sans a great favour, instead of simply taking what he was paying for. 

The was Sans was currently feeling though, it felt like a favour to him too. 

He wanted to cum. 

Mettaton stood up, without removing his hand or his fingers from where they were crammed up his pelvis. The wonders of extendable, flexible arms. Sans had never been more grateful for those jointless things than he was now. They were amazing. The best. He would die if the brushes in his sacrum and their delicious stimulation were removed. 

A hatch slid open on Mettaton’s crotch, metal plates elegantly folding aside like a complicated artwork of origami, to reveal a set of brightly glowing genitalia. They were partially mechanic, silvery like the rest of his robotic body, and partially made up of the same ectoplasmic flesh many monsters used to conjure their genitalia and other useful appendages. There was a metallic shaft encasing a ghostly pink dick, hard and leaking precum in smaller quantities than Sans’ did. Underneath it sat the slick, glistening lips of a plump cunt that had formed over an entrance riddled with nubs and ridges and other shapes that would surely feel interesting to rub against. 

Sans felt his cock twitch. 

That was new. Mettaton didn’t have those nubby things before, nor the metallic hull around his cock. His genitalia had been entirely ectoplasmic the last time they’d had sex. 

“Interesting, aren’t they?” Mettaton smiled. “I had them built to my own designs.” 

“th-they look great,” Sans stammered, sweat beginning to collect on his skull. 

“They’re made from brushed metal, that gives them the satin finish,” Mettaton bragged. “Without roughing them up. They feel _very_ smooth.”

“mettaton please,” Sans whined, not able to stand it for much longer. “please, I need you to fuck me. please.” 

“Patience, sweetie. I’m getting there,” Mettaton said casually, pushing Sans upwards. His legs were no longer dangling over the edge of the bed. He was now laying fully on the bed, sinking into the softness of the sheets a little. He felt as though he was drowning in it, the massive size dwarfing him. With Mettaton’s height added to it, it made him feel tiny. 

The brushes were still inside his sacral holes, driving him insane. 

Finally Mettaton climbed onto the bed as well, positioning himself above Sans’ cock. One of Mettaton’s arms was behind his back, the one whose hand was inserted into Sans’ pelvis. The other arm was moving forwards, the hand brushing over Sans’ spine. Both of their cocks throbbed when Sans moaned deeply and arched into the touch.

Mettaton began lowering himself onto Sans immediately, and he felt he could cry with relief when he felt the moisture of that plump pussy rub against the head of his cock. The slick juices made it easy to slip in, the cunt practically sucking his dick in. Sans cried out in relief, his head falling back as he was enveloped in the warm, sticky softness that was Mettaton’s cunt. The ridges and nubs that now lined the inside of the entrance made for an interesting feeling and he would have been perfectly content to come just like this, losing himself in the gentle massage. 

Then the ridges and nubs began to vibrate and move, actually beginning to massage the sensitive flesh of his cock. 

“wha - aaah, ah fuck, met - _ugh_!”

“Are you still… okay…?” Mettaton asked, breathing heavily. It was clear that by now, he was just as affected by their activities as Sans was. 

“g-green! green! keep going, oh fuck, oh fuck you, you’re so good, so good, so _good_ , aah, aaaaaah please please please - “ 

It was entirely too much; the ticklish sensation of the brushes in his sacral holes, the firm hand stroking his spine, the vibrations and massaging motions against his cock. He was thrusting upwards weakly, having little strength left in the overwhelming amount of stimulation he was receiving in three different places at once. 

Mettaton was moaning on top of him, riding his cock in wild abandon, their voices mingling in the small room. 

The pussy surrounding him constricted, pulsing rhythmically and sucking him in even deeper, to the hilt until he felt the head bump against the back of Mettaton’s magic. It was softer than anything, softer even than the plump lips hugging around the base of his shaft. 

A breathless cry bubbled out of Sans’ nonexistent throat, and he came, shuddering as his release filled the other up, a heated gush of fluids that swirled around where their magic met until it began to slip past their flesh and out of Mettaton, dribbling down Sans’ bones where their bodies were joined. 

Panting hard and feeling dizzy and weak, Sans blinked his eyes open only to find Mettaton staring down at him with barely concealed hunger in his eyes. He was licking his lips, face flushed and breathing just as hard; he must have come as well. 

Methodically, Mettaton removed himself. Pulled the brushes out of Sans’ sacral holes and the hand out of the pelvic inlet. Let go of the spine. Lifted himself up and released Sans’ cock, not minding the cum and other fluids that gushed out of his pussy at the separation. Mettaton stared down at Sans, eyes roaming over each single bone. 

He welcomed the brief respite, breathing deeply and taking the moment where nothing was touching him as a break he knew he needed. 

Sans was aware they weren’t done yet. 

Far from it. 

Mettaton had rather large amounts of energy that even the constant performances in front of a crowd couldn’t entirely dampen; no matter how much he danced, acted, or moved in general, there was always just a bit more left. The same was true in the bedroom. Mettaton did get tired, his supply of energy wasn’t endless, neither the electricity for his body or his mental energy lasted forever. It could take a while though. The fact that she shifted back to his boxy form promised that the robot intended to make this last.

“Turn around,” Mettaton ordered. 

With a tired huff, Sans followed the command, rolling over until he was lying on his front. 

“Close your eyes.” 

That was easy. His eyes practically obeyed all by themselves. It was only the knowledge that Mettaton wasn’t into somnophilia that made Sans force himself to stay awake. Hell, he’d love a client like that right about now. Drifting off to sleep while being fucked sounded like heaven right about now, especially if he would get paid for it. 

Hands began to stroke over his scapula and ribcage, exerting a gentle pressure before dipping into the gaps between the ribs. The fingers firmly rubbed the sturdy bones, moving from the strongest points where they joined the spine outwards and then back again. Sans groaned in pleasure, relishing the sensation. Attention was paid to his vertebrae as Mettaton’s hands moved downwards, towards the more sensitive regions of his body. Sans breathed out a low moan, rubbing his softened but still manifested cock against the bedsheet. 

“feels good,” he mumbled. “you feel so good…” 

A smug, self-satisfied bout of laughter sounded from somewhere above him. 

“Summon a cunt for me,” Mettaton commanded. 

Sans obeyed with a whine, feeling his pussy clench as soon as he manifested it. He felt empty. One of Mettaton’s hands made its way downwards and he thought he’d get penetrated, his desire fulfilled, but Mettaton seemed entirely content to play with the lips for now, teasing his finger over the slit and brushing against Sans’ clit without actually granting him the fulfilment he craved. 

“nnngh, please… “ he moaned. 

“Beg more,” Mettaton instructed.

“please, mettaton, please take me, i can’t stand it anymore… i feel empty… i need you. i wanna come, i wanna feel good, please, you can make me feel good, you feel amazing, you’re the best - “ Sans groaned when a finger was slipped in, leisurely and without care, not moving. 

It began to vibrate just enough to make the teasing even more unbearable and Sans began to sob, ribcage heaving with each wet, shuddering breath.

“Green?” Mettaton asked, pausing in his movements without stopping the vibrations. 

“g-green,” Sans confirmed, a noisy hiccup interrupting the word. 

“Aw,” Mettaton said. “You’re really cute when you cry.” 

And he removed his finger. 

“ _no_ , no please, mettaton, please, i’ve been good, i’ve begged, please don’t stop, make me come, fuck me, please,” Sans cried out, desperate to find the right words to make the other continue, desperate to get that stimulation on his cunt back. 

“It’s okay,” Mettaton assured him, using a deliberately soothing tone of voice that did nothing to help Sans in his desperation. The robot was holding onto his iliac crests, preventing him from at least rutting into the bedsheet as the only form of stimulation he could currently get. The bed dipped as Mettaton moved, creaked a little. 

The sensation of something warm and firm pressing against the lips of his cunt made Sans sob out even louder. 

“oh shit, yes, please fuck me, come on, do it already, please, fill me up…” 

To his absolute fucking delight, Mettaton complied without further teasing. He snapped forwards, hilting in Sans’ cunt in one go and making him scream his lust out loud. The cock began to vibrate inside of him and his sobs transformed into high-pitched moans, his sensitive ectoflesh twitching with the deep and hard thrusts into him. His cock was pressed against the fabric of the sheets, rubbing against it automatically with each movement. The double sensation from his pussy and his cock was a heady sort of pleasure, causing his eye lights to roll back into his sockets.

The bed creaked with their activity, a filthy sound that fitted the atmosphere. 

Halfway through, Sans felt Mettaton shift yet again, once more assuming his more humanoid form now that he had rested a bit and saved up the energy for it. Being able to better brace himself with two legs, his thrusts increased in strength. His body covered Sans fully as he leaned forwards, bringing his hands into the empty cavity of Sans’ ribcage. They too began vibrating, tipping him over the edge again. 

He screamed his orgasm half into the bedsheets and half into the room, hearing Mettaton curse behind him. Hot cum flooded his cunt and yet Mettaton didn’t stop moving, drawing their orgasms out. 

Mettaton collapsed on top of him. His humanoid body was heavy against Sans’ bones, but there was no energy left inside of him to care. He was sweaty and breathless, vocalising small, pleased moans on each exhale. It took a bit before Mettaton rolled off of him, lying on the back and shifting into his boxy form once more. 

Conserving energy for the next round. 

Sans shuddered. 

For a while, they simply laid next to each other, their gasps were all that was heard in the room. Sans felt truly exhausted and more than ready to sleep. He actually might have dozed off for a bit there, but not enough to truly sleep. He was startled out of it easily when Mettaton recovered more quickly than he did. 

“Make an asshole,” the robot ordered suddenly. 

Oh stars. 

Sans already knew what was coming and he wasn’t ready, which was to say that he was completely ready which kind of scared him. It was crazy how much he could enjoy his customers wrecking him thoroughly. The thought was exciting enough that he managed the feat despite the extra energy it cost him. 

Mettaton had already shifted into his human form for the third time this night, ready to take Sans once more. He positioned himself so his cock was hanging just above Sans’ mouth while Mettaton’s mouth was just above Sans’ cock. The breath ghosting over the ectoflesh was enough for his dick to twitch, hardening again. 

Sans felt a three fingers shoved unceremoniously into his still wet pussy, while another finger carefully wriggled inside his asshole. The tip of Mettaton’s cock was nudged against his teeth and he obediently opened his mouth, swallowing the other when he lowered himself down. He licked against the shaft and groaned with pleasure when Mettaton returned the favour on Sans’ cock. 

_Click._

The buzz of the vibrations springing to life. The fingers in his cunt and ass were vibrating, Mettaton’s cock was vibrating, his mouth and tongue were vibrating, his body was vibrating against Sans’ bones. He wanted to curse but his mouth was full. 

“Let’s go,” Mettaton purred. 

With a guttural sound of lust, Sans braced himself for a long, long night.


End file.
